Fiber-filled plastic compositions are widely used for making floor and wall tile, as well as for many other uses where the toughness which is imparted by fiber reinforcement is desired. In flexible fiber reinforced plastic compositions, asbestos fibers have been commonly used, and continue to be used because of their many advantages, despite the major disadvantage that asbestos fibers are carcinogenic. Thus, the manufacture of plastic formulations containing asbestos presents difficult safety problems for the manufacturer.
Accordingly, it would be desirable to substitute the asbestos fibers in flexible plastic tile formulations and the like with another fiber, for example, organic fibers such as polyester (Dacron) fibers. However, the use of such fibers on a commercial basis in plastic formulations has proven to be difficult, because the fibers have hitherto not dispersed easily throughout the plastic formulations during mixing. Accordingly, the finished products do not exhibit the desirable physical characteristics that one might expect from a fiber-reinforced plastic formulation. For example, the prior art finished products tend to exhibit insufficient tack, and thus do not adhere well to rollers for processing into sheet form.
In British Pat. No. 1,331,788, it is proposed to mix organic fibers into a plastic formulation for tile or the like, along with ground limestone particles (calcium carbonate) which generally range in particle size between 20 mesh and 200 mesh, to improve the structural properties of the tile such as abrasion resistance and hardness. However, the dispersion problem of organic fibers remains when ground limestone of this particle size is used, even when minor fractions of the limestone filler are smaller than 200 mesh.
In accordance with this invention, plastic formulations are disclosed in which an organic, fibrous filler may be more uniformly dispersed, avoiding visible clumps of fiber in the fiber formation. The plastic formulations of this invention may be mixed to uniformly disperse the fibers and avoid visible clumps of agglomerated fibers, without the use of an undesirably vigorous mixing procedure. Furthermore, plastic formulations which are tough and strong at room temperature, yet which are soft enough at elevated temperatures to be effectively rolled into sheeting of the desired thickness, are provided by this invention.
Furthermore, in accordance with this invention, less than 20 percent by weight of resin component can be effectively utilized in the formulations of this invention, which is considerably less resin than has been conventionally used in conjunction with asbestos-filled formulations. This can reduce the overall price of the formulations of this invention, when compared with asbestos formulations, since the resin component is generally one of the most expensive ingredients, on a per pound basis, used in plastic formulations.